Thrombocytopenia, a condition characterized by low platelet counts and excessive hemorrhage is a potentially fatal complication of many pathological states. The primary and virtually only effective treatment of this condition is periodic whole blood or platelet transfusions, the limitations of which are self evident. The humoral factor thought to be responsible for the proliferation and maturation of megakaryocytes and platelets, is thrombopoietin (TPO). Although the cDNA for TPO has recently been cloned, the structure of the gene and the regulation of its expression remain to be elucidated. The goal of this project is to identify drugs which can be orally administered and which are capable of stimulating the production of TPO by interacting with factors modulating its transcription. The experimental objective in Phase I includes (i) the construction of defined plasmid vectors, in which a reporter gene (luciferase) will be placed under the control of potential regulatory sites identified and derived from the flanking regions of the TPO gene, and (ii) the stable transfection of the TPO-luciferase fusions plasmids into human embryonic kidney and liver cell lines, that will serve in Phase II as target cells in an automated high throughput drug screen to identify stimulators of TPO expression. These cell lines will also provide exceptional laboratory models to examine the ability of various cytokines and other known effectors to serve as potential modulators of TPO expression. PROPOSED COMMERCIAL APPLICATION: The ultimate goal of the present proposal is to develop orally-administered drugs which stimulate TPO gene, to treat thrombocytopenia. This approach would circumvent the current problems associated with platelet transfusion, or with the potential administration of a biological. Estimates of the market potential for TPO are in the range of $1 bn annually.